Method of locating a subscriber unit within the coverage area of a communication system

Abstract

In a communication system ( 800 ) having transmitters ( 108 ) for transmitting location information to subscriber units ( 102 ) located with the transmitters' coverage areas, a method of determining the location of a subscriber unit. At least some of the transmitters use different assigned time intervals to transmit their information, and a subscriber unit receiving such information can determine its location based, at least in part, on the time interval during which it received information. Received location information is stored in a dedicated portion ( 808 ) of a subscriber unit's memory for later retrieval by the user. In a two-way system, a subscriber unit can transmit its stored location information to a system receiver ( 802 ) for storage in a system memory ( 804 ). The system memory ( 804 ) is accessed by a system operator or other authorized person to determine the location of a subscriber unit and/or its pattern of movement throughout the coverage areas.

What is claimed is:  
     
       1. A method of determining the location of a subscriber unit operating in a communication system having transmitters that transmit information to the subscriber unit, each transmitter transmitting substantially within its own coverage area, the method comprising: 
       causing at least some of the transmitters to use different assigned time intervals of a transmission cycle for transmitting information;  
       receiving, at the subscriber unit, information transmitted during at least one of the assigned time intervals;  
       identifying, at the subscriber unit, the coverage area of a transmitter from which received information was transmitted, based, at least in part, on which time interval was used to transmit the received information; and  
       storing an indication of an identified coverage area for later retrieval.  
     
     
       2. A method as set forth in  claim 1  wherein the communication system includes a receiver and a memory, wherein the subscriber unit stores location information sent by the transmitters, and further including: 
       causing the subscriber unit to transmit stored location information to the receiver; and  
       storing, in the memory, location information transmitted by the subscriber unit, thereby to record movement of the subscriber unit.  
     
     
       3. A method as set forth in  claim 1  wherein the transmitters are low power transmitters, and wherein the communication system includes a high power transmitter for transmitting throughout a large coverage area that substantially includes coverage areas of the low power transmitters, and where all the transmitters transmit on a common frequency. 
     
     
       4. A method as set forth in  claim 1  wherein the information transmitted includes an indicator for location information, wherein the subscriber unit includes a memory for holding information relating to location, and wherein the subscriber unit responds to the indicator by storing location information in the memory. 
     
     
       5. A method as set forth in  claim 4  wherein the transmitters transmit the indicator periodically. 
     
     
       6. A method as set forth in  claim 5  wherein the transmitters transmit a time stamp with the indicator, and wherein the subscriber unit stores the time stamp with location information. 
     
     
       7. A method of determining the location of a subscriber unit operating in a communication system having a high power transmitter for transmitting information throughout a wide coverage area, and having low power transmitters for transmitting information within their own smaller coverage areas located substantially within the wide coverage area, the method comprising: 
       causing the high power transmitter and the low power transmitters to repeatedly transmit information throughout their respective coverage areas, the transmitters using a common frequency and different assigned frames of a transmission cycle for transmitting information, and the information transmitted by the low power transmitters including an indicator for location information and a time stamp; and  
       at the subscriber unit:  
       receiving information transmitted during at least one of the assigned frames;  
       identifying a coverage area from which received information was transmitted, based, at least in part on which frame was used to transmit the received information;  
       and storing location information, including the identity of an identified coverage area with a time stamp for later retrieval.  
     
     
       8. A method as set forth in  claim 7  wherein the communication system includes a receiver and a memory, and further including: 
       causing the subscriber unit to transmit stored location information to the receiver; and  
       storing, in the memory, location information transmitted by the subscriber unit.  
     
     
       9. A method of tracking the movement of a subscriber unit operating in a communication system having transmitters that are located in different coverage areas and that use different frames of a transmission cycle to transmit information on a common frequency, the method comprising, in the subscriber unit: 
       receiving transmitted information;  
       identifying a coverage area from which received information was transmitted, based, at least in part, on which frame was used to transmit the received information; and  
       storing an indication of an identified coverage area for later retrieval.  
     
     
       10. A method as set forth in  claim 9 , including: 
       storing successive indications of identified areas as the subscriber unit moves from coverage area to coverage area; and  
       displaying, at user demand, at least a most recently stored indication to show the subscriber unit's current location.  
     
     
       11. A method as set forth in  claim 9  wherein the communication system includes a receiver, and further including causing the subscriber unit to periodically transmit, to the receiver, stored indications of identified areas. 
     
     
       12. A method as set forth in  claim 11  including transmitting a time stamp with a transmitted indication. 
     
     
       13. A method as set forth in  claim 9  wherein the communication system includes a receiver and a memory, wherein a transmitter sends location queries to subscriber units, and further including causing the subscriber unit to respond to a location query by transmitting at least one stored indication to the receiver for storage in the memory. 
     
     
       14. A method of tracking the movement of a subscriber unit operating in a communication system having a receiver and having transmitters that are located in different areas and that use different frames of a transmission cycle to transmit information on a common frequency, the method comprising, in the subscriber unit: 
       receiving transmitted information;  
       identifying a coverage area from which the received information was transmitted based, at least in part, on which frame was used to transmit the received information;  
       storing indications of identified coverage areas, and storing a time stamp with each such indication; and  
       transmitting to the receiver at least a most recently stored indication of an identified coverage area.